Failing test for URL-encoded access tokens

Facebook doesn't use JSON, see https://github.com/idan/oauthlib/issues/267.
Implement URL-encoding fallback for access tokens
Failing test for expires as alias for expires_in
Support expires as an alias for expires_in
Failing test for token_type relaxation
Relax token_type checking
Add documentation of OAUTHLIB_STRICT_TOKEN_TYPE
Merge pull request #268 from whit537/facebook

work around Facebook's non-conformance